In early research devoted to the first systematic investigation of marine animals as new sources of potential anticancer drugs the phylum Porifera rapidly became of increasing importance. Subsequent detection of antineoplastic activity in some of these sponge species led to the isolation of such cell growth inhibitory compounds, as macrocyclic lactones, pyrroles, peptides, and proteins. Meanwhile the isolation of heterocyclic marine sponge constituents such as pyrroles, imidazoles, oxazoles, indoles, pyridines, quinolizidines, pteridines, acridines, other nitrogen systems and quinones has been rapidly accelerating. So far ten isoquinolinequinones have been isolated from blue species of the sponge genera Reniera and Xestospongia. In 1986 an exploratory survey of marine Porifera off remote islands in the Republic of the Maldives was conducted which located a deep blue colored specimen of Cribrochalina sp. (Haplosclerida order) that afforded an orange ethanol extract. The encrusting sponge was found in areas of strong (and dangerous) currents to -45 m in the South side of East reef passages and yielded and ethanol extract that provided 40% life extension (at mg/kg) against the U.S. National Cancer Institute's in vivo murine P388 lymphocytic leukemia (PS system). Bioassay directed isolation using the in vitro PS leukemia led to the discovery of new cytostatic isoquinolinequinones designated cribrostatin 1 and cribrostatin 2.